Toolcraft probably makes more BCGs than any other manufacturer in the USA, and they are excellent quality. The company's components are so reliable that many of the big USA gun brands will not bother making their own BCG, they simply order them from Toolcraft and add their own brand name.

The bolt is made from 9310 steel, a more modern tool steel compared to the classic carpenter steel. It is a nickel-chrome-molybdenum case-hardening steel, with good strength and toughness properties. It has high hardenability, high core hardness and high fatigue strength. 9310 steel is typically used in components with large cross sections requiring high toughness and core strength such as gears, crankshafts and heavy-duty gear shafts in aircraft and truck construction.

Link to parts manufacturer